1. Field of the Invention
The present invention relates to systems and processes used in manufacturing integrated device die, such as integrated circuit and laser die, including diode laser die, formed on sapphire substrates. More particularly, the present invention provides for scribing sapphire substrates using solid state UV lasers, and separating the scribed sapphire substrate into die.
2. Description of Related Art
Sapphire Al2O3 is used as a substrate for a variety of devices. The sapphire is a hard material that is optically transmissive, electrically nonconducting and a good conductor of heat. It has become the preferred substrate material in manufacturing of laser diodes. In particular, blue laser diodes and other structures based on gallium nitride GaN and related materials are manufactured on sapphire substrates in large volume.
One bottleneck in manufacturing of die on sapphire substrates is the separation of the die from the substrate. Because sapphire is very hard, the typical process requires the use of a diamond tipped blade to scribe a pattern in the substrate. In one common method, the sapphire substrate having an array of semiconductor structures such as laser diodes formed thereon is placed on an adhesive known as xe2x80x9cblue tape,xe2x80x9d or xe2x80x9cwafer tape.xe2x80x9d A diamond blade is used to scribe the substrate. Mechanical stress is used to crack the substrate along scribe lines. The tape carrying the cracked substrate is then stretched to separate the die. A robotic pick and place machine is used to remove the individual die, having typical dimensions in a range of 200 to 500 microns on a side, from the tape.
One major bottleneck in the manufacturing of the die is the cutting process. The diamond blade requires the manufacturer to allocate a relatively wide scribe line, referred to as a xe2x80x9cstreet,xe2x80x9d (for example, 40 to 70 microns) on the substrate, reducing the number of die manufacturable on a single substrate. In addition, the diamond tip blade must be operated relatively slowly, requiring as much as 1 and a half hours for a 2 inch diameter substrate. Also, the diamond tips on the blade wear out and must be replaced often, as much as one blade per wafer. Replacement of the blades slows down the process of manufacturing. Also, the blades typically have multiple tips, which must be carefully and precisely aligned for proper cutting each time a new tip is brought on line, and each time a new blade is installed. Finally, the mechanical scribing process causes cracks, which can damage the die and reduce yields. Typical yields for this process have been reported to be about 70%.
It is desirable, therefore, to provide a system and method for scribing sapphire substrates in manufacturing die which is faster, easier to use, minimizes the number of consumable parts, allows for greater density and achieves greater yields than is available using current technologies. Further, it is desirable that such system be compact, safe to operate and low-cost.
The present invention provides a method and system for manufacturing integrated device die, such as diode laser die, from a sapphire substrate carrying an array of such integrated devices. Particularly, the present invention is suitable for manufacturing blue laser diodes based on gallium nitride structures. According to the present invention, greater density and greater yield are achieved, while also reducing the time required to separate the individual die from the substrate. Furthermore, the present invention is based on compact, low-cost machines, and otherwise reduces the overall manufacturing costs for such integrated device die.
The present invention provides a process including mounting a sapphire substrate, carrying an array of integrated devices, on a stage such as a movable X-Y stage including a vacuum chuck. Next, pulses of laser energy are directed at a surface of the sapphire substrate using a solid-state laser. The pulses of laser energy have a wavelength below about 560 nanometers, and preferably between about 150 and 560 nanometers. In addition, energy density, spot size, and pulse duration are established at levels sufficient to induce ablation of sapphire. Control of the system, such as by moving the stage with a stationary beam path for the pulses, causes the pulses to contact the sapphire substrate in a scribe pattern at a rate of motion causing overlap of successive pulses sufficient to cut scribe lines in the sapphire substrate.
Embodiments of the present invention produce laser pulses having an energy density between about 10 and 100 joules per square centimeter, a pulse duration between about 10 and 30 nanoseconds, and a spot size between about 5 and 25 microns. The repetition rate for the pulses is greater than 5 kHz, and preferably ranges from about 10 kHz to 50 kHz or higher. The stage is moved at a rate of motion causing overlap of the pulses in the amount of 50 to 99 percent. By controlling the pulse rate, the rate of motion of the stage, and the energy density, the depth of the scribe line can be precisely controlled. In embodiments of the invention, the scribe lines are cut to a depth of about one-half the thickness, or more, of the sapphire substrate, so that for an 80 micron thick substrate, the scribe line is cut to a depth in the range of about 35 microns to, for example, 60 microns, and more preferably greater than 40 microns.
In embodiments of the present invention, the solid-state laser comprises a diode pumped, Q-switched, Nd:YVO4 laser, including harmonic frequency generators such as nonlinear crystals like LBO, so that output of the laser is provided at one of the second, third, fourth and fifth harmonic frequencies of the 1064 nanometer line produced by the neodymium doped, solid-state laser. In particular systems, the third harmonic frequency of about 355 nanometers is provided. In other embodiments, the solid-state laser comprises a Q-switched, Nd:YAG laser, operating to provide one of the harmonic frequencies as output.
In embodiments of the invention, the method includes detecting edges of the sapphire substrate while directing pulses at the substrate in the scribe pattern. In response to detected edges, the system prevents the pulses of radiation from being directed off of the substrate.
Embodiments of the present invention direct the pulses of radiation at the backside of the substrate. This prevents damage potentially caused by heat from reaching the active integrated device die structures. Furthermore, it prevents debris from the ablation process from contaminating the integrated devices on the die.
Thus, embodiments of the invention include placing the top surface of the substrate on an adhesive tape prior to scribing, mounting the substrate with the adhesive tape on the stage, moving the substrate under conditions causing ablation of the sapphire in a scribe pattern on the backside of the substrate, and detecting edges of the substrate during the scribing process to prevent the pulses of radiation from impacting the adhesive tape.
The die defined by a scribe pattern are separated from the sapphire substrate, by mechanically cracking the substrate along the scribe lines, and using a pick and place robot or other technology known in the art. In one embodiment, the sapphire substrate is placed on an adhesive tape prior to scribing, and after scribing the substrate is rolled or otherwise mechanically manipulated to break the substrate along scribe lines in the scribe pattern. The separated die remain adhered to the adhesive tape, until separated using the pick and place robot, or other technology.
Embodiments of the invention further provide for controlling polarization of the laser pulses with respect to direction of scribe lines in the scribe pattern. The polarization is controlled so that the grooves are more uniform for scribe lines parallel to different axes. Uniformity can be improved by random or circular polarization of the pulses in some embodiments. More preferably, polarization of the pulse is controlled so that the polarization is linear and parallel to the scribe line being cut. It is found that the quality of the groove being formed is more V-shaped with parallel polarization, and more U-shaped with polarization that is not aligned. V-shaped grooves are preferred for more uniform and predictable breaking of the substrate during separation of the die. Embodiments of the invention provide for control of the polarization using a laser with an adjustable polarizer, such as a half wave plate, in the optical path.
The invention also provides a system for scribing sapphire which comprises a solid-state laser, as described above, a stage adapted to support and move a sapphire substrate, optics directing pulses to impact of sapphire substrate mounted on the stage, an edge detection system which detects edges of substrate mounted on the stage during movement of the stage, and a control system. The control system in embodiments of the invention comprises a computer system coupled to the solid-state laser, the stage, and the edge detection system. The computer is responsive to the edge detection system and parameters set by users to cause the pulses to impact of the sapphire substrate in a scribe pattern at a rate of motion causing overlap of successive pulses sufficient to cut scribe lines in the sapphire substrate. Embodiments of the invention also include a debris exhaust system coupled with the stage.
Embodiments of the invention include a user interface with logic to set up the scribe pattern, and the operational parameters including pulse repetition rate, stage velocity and energy levels to establish scribe depth, scribe speed and other characteristics of the process.